This invention relates to apparatus and method for cutting and more particularly the mounting of cutting blades in a rotating cylinder for cutting or perforating continuous webs of paper, plastic, fabric, etc. More specifically, the invention applies to the manner in which the cutting blade is supported, clamped, and changed.
In the manufacture of many articles of paper, plastic, fabric and the like, there is a need to cut or perforate across the width of a moving web. A widely used method of doing this is to use steel rule cutting blades clamped in a slot of a rotating cylinder or roll. The blades cut against a hardened steel impression cylinder or roll. A plurality of cutting rules are mounted around the circumference of the cylinder. The blades are first clamped lightly, the cylinder rotated one revolution to seat each blade in contact with the impression cylinder, then the blades are securely clamped before cutting any paper, plastic, fabric, etc.
This method works quite well and has been in common use for many years. It does have some objections, however. First, as the speed of machinery has increased, a problem developed due to the heat generated in the bearings of the blade and impression cylinders. This heating causes the frames of the machine supporting the cylinders to expand--thus separating the centers of the cylinders and causing poor cutting for lack of sufficient contact between the cutting blade and the impression cylinder. This problem has been solved at some expense by providing heaters for the frames to maintain them at a uniform elevated temperature.
A second problem is the long time it takes to install new blades. The blades are typically held by a series of clamping screws each one of which must be set to a proper torque for the first revolution of the cylinder, and then tightened for the final clamping. If the torque for the first setting is too low, the blades will not cut. If it is too high, the blades will hit too hard giving short blade life and severe wear and tear on the bearings, drive gears, etc. If the blades are extended too far out of the blade cylinder slot for the first revolution, they can be permanently bent, and thus ruined--as a bent blade will not cut cleanly. The difficulty of setting cutting blades by this method results in many blades being set improperly requiring resetting, short blade life or poor quality cuts.
Prior art concerned with the solution of these problems includes U.S. Pat. No. 3,793,918 which discloses a method of clamping along the length of the blade by means of a plurality of cylindrical locking pieces actuated to apply a blade locking pressure by means of a single wedge in order to reduce the lock up time. U.S. Pat. Nos. 3,865,164, 3,989,077 and 4,068,694 show methods of spring loading wedge shaped clamping bars and U.S. Pat. Nos. 4,594,928 and 4,671,154 use pressure cylinders to provide the clamping force. All these patents rigidly clamp the blade and deal only with the problem of reducing the time to change the blades More recently U.S. Pat. Nos. 4,848,202 and 4,902,843 also show method of quick change mounting of blades. U.S. Pat. No. 4,848,202 provides for shimming under the clamping bar to adjust for inaccuracies in machining or tolerances while U.S. Pat. No. 4,920,843 provides for operator adjustment screws for each blade to compensate for these differences in blade height.
U.S. Pat. No. 4,143,568 shows a resilient mounting of the cutting blade so that the blade or its mounting can be flexed to the extent necessary to develop the required cutting force using the spring rate of the blade to avoid the rolling in "process" to adjust the height of the blade. Again this patent addresses only one of the several problems.
U.S. Pat. No. 4,444,080 shows a blade made to be elastically deformable to enable at least a portion of the blade to yield as it engages the hard surface of the impression cylinder. Here the means provided to enable the deformation, require that the blade be clamped along only the lowermost portion of the blade which leaves the cutting edge of the blade poorly supported.
None of the prior art provides a cutting blade support and clamping system that meets the objectives of this invention. In particular, none of the prior art provides restraint to the movement of the blade across the width of the cylinder while clamped with reduced spring force.